The present invention is directed generally to optical microscopy and in particular addresses the need to handle a sample that has two or more small areas that need to be measured, which are too far apart to fall on the detector but are within the field of view of the objective or measure a long, narrow strip that is too long for the detector, but whose total area is less than the detector area.
In the design of optical inspection equipment, it is necessary to balance cost and flexibility of the instrument. A great deal of optical inspection equipment is based upon commercially available microscopes or microscope objectives and an electronic area detector (see FIG. 1). However, the designs of most optical microscope objectives permit their use in a visual instrument. Industrial and biological microscopes made by manufacturers such as Nikon, Olympus, Zeiss and Leica, produce images of good quality with a 20 to 25-mm diameter. The eyepieces used on these microscopes further magnify the 20 to 25-mm diameter image for viewing by the eye.
In many industrial applications, an array detector such as a CCD camera is placed at the image plane rather than an eyepiece. Typical CCD detectors have a rectangular outline and fit within an 8-mm diameter circle (xc2xd inch format). It is possible, in many applications to select an objective and detector such that sufficient resolution is obtained over a large enough area. However, there are cases in which the area on a sample to be tested does not fit within the detector area but does fit within the field of view of the objective. Simply put, the detector is too small.
One solution to the problem of a too small detector is simple: buy a bigger detector; however, this solution can be cost prohibitive as well as too slow because of reduced detector frame rates. Another solution is to build a mosaic of small detectors to fill the required image area. Of course, one may also scan the sample, building up a mosaic of data sets that must be registered via computer processing. However, scanning a sample greatly increases the required, hardware, software and time required to measure a sample.
What is needed is an optical system that can handle a sample that has two or more small areas that need to be measured, which are too far apart to fall on the detector but are within the field of view of the objective. Similarly, what is needed is an optical system that is capable of measuring a long, narrow strip that is too long for the detector, but whose total area is less than the detector area.
In accordance with the present invention, rather than using a large CCD camera or multiple CCD cameras to meet the above-stated needs, a dual field of view optical system and a single, lower cost detector are utilized.
Specifically, a dual field of view optical system for use in a microscope comprising: (1) an illuminator arm with an illumination source, (2) a beam splitter, (3) an objective, (4) a sample plane for location of a sample to be observed, (5) a detector arm including a detector located at an image plane, with the illuminator arm configured to illuminate the sample plane through the beam splitter and the objective and with the detector arm configured to receive an image of the sample and including the dual field of view optical system, and either (6a) a field stop in the illumination arm or (6b) a field stop at the image plane with additional relay optics. The dual field of view optical system comprises two beam splitters, two mirrors and one detector, with the two beam splitters in the same plane and the mirrors disposed on either side of the beam splitters, an entrance portion for receiving the image from the sample and an exit portion for directing the image onto the detector.
Further in accordance with the present invention, a microscope comprising the elements enumerated above further comprises the dual field of view optical system. Alternatively, an interferometer comprising (1) suitable imaging optics in place of the objective and (2) a reference arm may be constructed employing the dual field of view optical system.
The dual field of view optical system permits (1) viewing a sample that has two or more small areas that need to be measured, which are too far apart to fall on the detector but are within the field of view of the objective and (2) measuring a long, narrow strip that is too long for the detector, but whose total area is less than the detector area.